This invention relates to a method for separating leukocytes from a leukocyte-containing suspension by filtration, and to a filter unit used therefor.
By the term "leukocyte-containing suspension" used herein is meant blood, ascites, bone marrow and other leukocyte- or leukocyte precursor cell-containing body fluids. This term should also be interpreted as including physically, chemically and/or biologically treated blood and other body fluids such as, for example, blood diluted with a physiological solution, erythrocyte agglutinant-(such as dextran or hydroxyethyl-starch)-incorporated blood, a buffy coat and other leukocyte-containing suspension layers prepared by centrifugation or cell-electrophoresis.
In recent years component transfusions have often been employed in place of whole blood transfusions. Component transfusions involve transfusing the particular blood components needed or desired for the patients, and are advantageous in that the needed components, separated from unneeded or injurious components, are administered in a desirably high concentration. Particularly, a leukocyte or granulocyte transfusion for infected leukopenic patients and a leukocyte-poor, erythrocyte-rich blood transfusion for preventing graft versus host (GVH) reaction from occurring due to imcompatibility of histocompatibility antigens are now in frequent use.
It is also a popular practice to prepare leukocyte or erythrocyte suspensions of a high purity for the purpose of studying blood cells.
Various processes have been employed for carrying out leukocyte separation. Typical separation processes include, for example, an agglutinant incorporation-sedimentation process, a centrifugation process and a filtration process utilizing a filter composed of a leukocyte-adherent material. The agglutinant incorporation-sedimentation process involves incorporating an erythrocyte agglutinant such as dextran or hydroxyethyl-starch into a leukocyte-containing suspension, and then subjecting the agglutinant incorporated liquid to sedimentation to separate the liquid into an erythrocyte sediment and a leukocyte-containing liquid layer. This process has several disadvantages in that it requires a substantial period of time for the separation to be completed, in that the resulting leukocyte suspension is of a low purity, and in that it is often required to remove the agglutinant from the resulting leukocyte suspension. The centrifugation process involves, for example, placing a plurality of liquids of different densities, one upon another, in a vessel to form density gradient superposed layers; placing blood on the top liquid layer; and then centrifuging the superposed layers thereby to separate the blood into several layers. This centrifugation process is not suitable for the separation of a large amount of blood. The filtration process involves passing blood through a filter composed of a leukocyte-adherent material such as polyamide fibers, polyester fibers, siliconized glass wool and absorbent cotton thereby to entrap granulocytes and monocytes in the filter, and then passing a physiological solution through the filter to collect the entrapped leukocyte components. This filtration process is not suitable for the separation of lymphocytes, particularly for collecting a lymphocyte-rich suspension of a high purity.